The result is this, there's a distance between the individual renderables:

When I make the worldspace position of the renderables the same as the world pos of the whole instance, the result looks as expected. But that doesn't match up the theory and doesn't give me correct results for light culling, because the world position is then used to check the distance to point lights, which gives incorrect large distances for renderables that are far away from the center of the complete mesh instance.